The present invention relates to compositions consisting essentially of dense microsphere (DMS) components. The invention also relates to methods for detecting components of DMS in blood, cerebrospinal fluid and other body fluids that result from the disruption of DMS in the brain parenchyma. More specifically, the present invention relates to the correlation of the presence of DMS components in such fluids and the onset or progression of the cerebral amyloid formation associated with Alzheimer's disease and related conditions.
The methodology of the present invention is useful for diagnosing cerebral amyloidosis and, consequently, the onset and progression of Alzheimer's disease and related conditions and for monitoring the progression of such disease conditions and the effectiveness of therapeutic regimes. In particular, the present invention relates to methods for the detection of protein and non-protein components of DMS and antibodies thereto which, when detected in cerebrospinal fluid, blood or other body fluids, signal the onset or progression of cerebral amyloid plaque formation.
Classified under the rubric "amyloidosis" are a number of pathological conditions characterized by the deposition of abnormal fibrils ("amyloid fibrils") in extracellular spaces. The amyloid fibril, in turn, represents a final common pathway for a diverse array of proteins. Regardless of their biochemical composition, however, all types of amyloid fibrils share (a) a .beta.-pleated sheet structure, (b) green birefringence under polarized light after staining with Congo Red dye, and (c) a fibrillar morphology which has a typical electron-microscopic appearance.
The deposition of amyloid fibrils can affect several organs in the systemic forms of the disorder, exemplified by familial Mediterranean fever, familial amyloid polyneuropathy and systemic amyloidosis, or it can be restricted to one organ in localized forms. Among the latter are conditions classified under the rubric "cerebral amyloidosis," which covers the Alzheimer group of diseases, namely, Alzheimer's disease [pre-senile dementia, senile dementia]; Alzheimer's disease associated with Down'syndrome; Alzheimer's disease associated with other central-nervous-system diseases, such as Parkinson's disorder; and congophilic angiopathy [associated or not associated with Alzheimer's disease]. Alzheimer's disease in general is an incurable brain disease affecting middle aged and elderly people throughout the world. According to most recent estimates, it is the fourth or fifth leading cause of death among North Americans, and is responsible for inestimable personal and social tragedy, loss of productivity, and custodial burden to society. There is presently no widely-accepted effective treatment for Alzheimer's disease.
The principle symptom (manifestation) of Alzheimer's disease is the loss of higher mental faculties, typified by the loss of memory and behavior referred to as "dementia." Dementia is a symptom or syndrome that can be seen in many brain diseases other than Alzheimer's disease, such as stroke, encephalitis and metabolic diseases. Since memory loss and dementia are relatively nonspecific symptoms, a certain and specific definition of Alzheimer's disease is based on the characteristic microscopic state of the brain, described initially by Marinesco, Alzheimer and others. See Alzheimer, A., Allegemeine Zeitschrift fur Psychiatrie 64:146-148 (1907); Marinesco, G., Comptes Rendus des Seances de la Societe de Biologie et ses Filiales 70:606-608 (1911).
The particular microscopic feature that is a universally accepted indicator of Alzheimer's disease, and that separates Alzheimer's disease from other causes of dementia, is the accumulation of large numbers of brain lesions referred to as senile or amyloid plaques and neurofibrillary tangles. Senile or amyloid plaques are spherical, ranging from 10 to 200 .mu.m in diameter, and while found only occasionally in aged adult cerebral cortex, are found in large numbers in Alzheimer-affected cortex. These lesions, when found in suitable quantity in a brain sample, are the definitive criteria for the diagnosis of Alzheimer's disease.
The clinical diagnosis of Alzheimer's disease often is a difficult and imperfect task that generally relies initially on ruling out other treatable or clinically definable causes of dementia. In the appropriate clinical context, if the latter causes cannot be proven, Alzheimer's disease is often diagnosed antemortem, by exclusion, as the most probable diagnosis. Many indirect methods of diagnosis at present are being proposed and tested. See Conference Report, Khachaturian, Z., Arch. Neurol. 42:1097-1105 (1985). But the only certain and acceptable method for diagnosing Alzheimer's disease is by tissue microscopic histological study of a brain biopsy or necropsy sample, in which the above-mentioned sine qua non lesions are recognized by a certified specialist.
Amyloid plaques in large quantities are essentially found only in the Alzheimer group of diseases, whereas neurofibrillary tangles are nonspecific and are found in at least ten other neurological diseases. See Corsellis, J.A.N., GREENFIELD'S NEUROOPATHOLOGY 951-1025 (4th ed. 1984) (Edward Arnold, London). Individual amyloid plaques have roughly 1000.times. the volume of individual neurofibrillary tangles. True measurements of total brain amyloid plaque and neurofibrillary content are not available, but on the above basis it is likely that the volume of abnormal brain tissue occupied by amyloid plaques is many hundreds of times that of neurofibrillary tangles. The essential feature of the amyloid plaque is the presence of amyloid fibrils, which are a congophilic red-green birefringent microfibrillar material. Corsellis, loc. cit.
A microscopic structure referred to as the dense microsphere (DMS) is known to exist in normal brain and in brain affected by Alzheimer's disease. See Averback, Acta Neuropathol. 61:148-52 (1983); results confirmed by Hara, J. Neuropath. Exp. Neurol. 45(2):169-178 (1986). Some specialists believe that DMS are linked to cerebral amyloid plaques as the source or as a precursor to the cerebral amyloid characteristic of Alzheimer's disease and related conditions. Evidence for the existence of DMS comes from microscopic histological section studies of fixed whole brain tissue, where the dense microspheres are seen to have a proteinaceous internal or central region ("DMS protein") Surrounded by continuous membrane ("DMS membrane"). The dense microspheres are observed as randomly dispersed, highly infrequent structures occupying an estimated 10.sup.-9 or less of total brain volume, at a unit frequency roughly estimated at 10.sup.-16 or less, relative to other definable brain structures such as mitochondria.
Neither the extraction, purification and characterization of isolated samples of DMS nor the use of DMS material to any advantage has been documented. Thus, DMS and its respective components are structures of unproven function and unknown significance or usefulness, and have been effectively unavailable in tangible form.
Moreover, non-surgical procedures for the antemortem diagnosis of cerebral amyloid plaque formation and, consequently, Alzheimer's disease and related conditions have heretofore been limited to the exclusionary process of diagnosis. Confirmation of such disease conditions has been possible only through analysis of brain tissue obtained by biopsy or at autopsy. Immunological methods universally accepted as diagnostic of Alzheimer's disease and related conditions have not heretofore been documented.